The present invention relates to an electric-discharge lamp lighting apparatus in which voltage applied to an electric-discharge lamp is generated by using a transformer.
FIG. 1 is a circuit view showing a conventional electric-discharge lamp lighting apparatus disclosed in the Published Unexamined Japanese Patent Application No. 2000-12273. In FIG. 1, 1 indicates a direct-current power source (12 V). 2 indicates an LC filter. 3a indicates a primary winding connected with the direct-current power source 1. 4a indicates a primary winding connected with the direct-current power source 1. 3b indicates a secondary winding for rising a level of voltage generated in the primary winding 3a. 4b indicates a secondary winding for rising a level of voltage generated in the primary winding 4a. 3 indicates a transformer. 4 indicates a transformer.
5 indicates a smoothing circuit for smoothing a level of voltage generated in the secondary winding 3b and a level of voltage generated in the secondary winding 4b. 6 indicates an H-bridge circuit for inverting a polarity of a current supplied to an electric-discharge lamp 8. 7 indicates a high-voltage generating circuit for generating a high voltage (about 20 kV) required to light the electric-discharge lamp 8. 8 indicates the electric-discharge lamp (HID) boarded on a vehicle. For example, a halogen lamp generally used as an electric-discharge lamp has a luminance ranging from 1000 to 1500 lm. In contrast, the electric-discharge lamp 8 has a luminance of 3200 lm, so that the electric-discharge lamp 8 is a very bright lamp.
9 indicates a transistor for performing an on-off control to apply a voltage or no voltage to the primary winding 3a. 10 indicates a transistor for performing an on-off control to apply a voltage or no voltage to the primary winding 4a. 11 indicates an inverter for inverting a chopping wave. 12 indicates a feed-back circuit for generating a feed-back voltage. 13 indicates a comparing circuit for comparing a voltage level of the chopping wave and a level of the feed-back voltage generated by the feed-back circuit 12 and outputting a control signal to the transistor 9. 14 indicates a comparing circuit for comparing a voltage level of the chopping wave inverted by the inverter 11 and a level of the feed-back voltage generated by the feed-back circuit 12 and outputting a control signal to the transistor 9.
Next, an operation will be described below.
A power source voltage of the direct-current power source 1 is applied to the primary windings 3a and 4a of the transformers 3 and 4. When an on-off control (or a chopping control) for the power source voltage is performed by the transistors 9 and 10, a risen-up voltage higher than the power source voltage is generated in the secondary windings 3b and 4b of the transformers 3 and 4. A current of the risen-up voltage higher than the power source voltage generated in the secondary windings 3b and 4b of the transformers 3 and 4 is smoothed in the smoothing circuit 5, and the risen-up voltage is applied to the electric-discharge lamp 8 while inverting the polarity of the current of the risen-up voltage in the H-bridge circuit 6. Also, because a high voltage of about 20 kV is required to light the electric-discharge lamp 8, the risen-up voltage is applied to the electric-discharge lamp 8 through the high-voltage generating circuit 7.
Here, control signals for the transistors 9 and 10 are produced as follows.
A chopping wave used as a reference wave is inverted in the inverter 11 and is supplied to the comparing circuit 14. In the comparing circuit 13, a voltage level of the chopping wave not inverted is compared with a level of the feed-back voltage generated by the feed-back circuit 12, and a control signal is output to the transistor 9. Also, in the comparing circuit 14, a voltage level of the chopping wave inverted in the inverter 11 is compared with a level of the feed-back voltage generated by the feed-back circuit 12, and a control signal is output to the transistor 10.
Therefore, the control signals have phases shifted from each other by 180 degrees and are supplied to the transistors 9 and 10.
Because the conventional electric-discharge lamp lighting apparatus has the above-described configuration, the chopping wave used as a reference wave is inverted in the inverter 11 to generate the control signals having phases shifted from each other by 180 degrees and to supply the control signals to the transistors 9 and 10. However, the chopping wave cannot be preferably inverted in the inverter 11.
Also, there is another configuration in which an operation amplifier (or an inverting amplifier) is used in place of the inverter 11 to invert the chopping wave used as a reference wave in the operation amplifier. However, to obtain an inverted chopping wave symmetric to the chopping wave used as a reference wave, it is required to perform an inversion operation within a time-period in which the operation amplifier can follow to the chopping wave. Therefore, when a chopping wave having a high frequency is input to the operation amplifier, the operation amplifier cannot follow a leading edge or a trailing edge of the chopping wave, the amplified chopping wave having a level gradually changed is output from the operation amplifier, a wave height value of the inverted chopping wave is lowered, and the symmetry between the inverted chopping wave and the chopping wave used as a reference wave is undesirably lost.
In general, in a widely-used operation amplifier manufactured at low cost, to obtain an inverted chopping wave symmetric to the chopping wave used as a reference wave, the maximum of a frequency of the chopping wave is limited to tens kHz. In contrast, to operate the conventional electric-discharge lamp lighting apparatus shown in FIG. 1, it is required to operate the conventional electric-discharge lamp lighting apparatus at a high speed corresponding to a frequency higher than tens kHz. Therefore, to follow to each input pulse of a chopping wave having a high frequency, it is undesirably required to use an expensive operation amplifier operative at high frequency.
Also, in case of the operation of an electric-discharge lamp lighting apparatus having the transformers 3 and 4 and the transistors 9 and 10 shown in FIG. 1, when a duty ratio of the control signal used for the on-off control of the transistor 9 considerably differs from a duty ratio of the control signal used for the on-off control of the transistor 10, an electric power and loss loaded on the transformer 3 is unbalance with that on the transformer 4. Therefore, it is undesirably required to use the transformers 3 and 4 and the transistors 9 and 10 respectively having a surplus size for the operation of the electric-discharge lamp lighting apparatus, and a problem has arisen that an electric-discharge lamp lighting apparatus having a small size cannot be manufactured at low cost.
As another technical literature relating to the prior art, the Published Unexamined Japanese Patent Application No. H10-25775 (1998) is known.
The present invention is provided to solve the above-described problem, and the object of the present invention is to provide an electric-discharge lamp lighting apparatus which is manufactured at low cost and is operated at high speed operation without using a circuit for inverting a chopping wave used as a reference wave.
An electric-discharge lamp lighting apparatus according to the present invention written in claim 1 of xe2x80x9cWHAT IS CLAIMED ISxe2x80x9d includes a referential rectangular wave generating circuit for generating a referential rectangular wave, an inverting circuit for inverting the referential rectangular wave generated in the referential rectangular wave generating circuit, a first integrating circuit and a second integrating circuit for integrating a level of the referential rectangular wave generated in the referential rectangular wave generating circuit and a level of a rectangular wave inverted in the inverting circuit respectively and producing chopping waves respectively, and a first comparing circuit and a second comparing circuit for comparing levels of the chopping waves produced in the first integrating circuit and the second integrating circuit with a feed-back voltage sent from a feed-back circuit respectively and outputting control signals to a first switching circuit and a second switching circuit respectively.
Therefore, because the chopping waves inverted to each other are produced in the first integrating circuit and the second integrating circuit after the referential rectangular wave is inverted in the inverting circuit, an electric-discharge lamp lighting apparatus operable at high speed can be obtained at low cost without using a circuit for inverting any chopping wave.
An electric-discharge lamp lighting apparatus according to the present invention written in claim 2 of xe2x80x9cWHAT IS CLAIMED ISxe2x80x9d includes a referential rectangular wave generating circuit for generating a referential rectangular wave, a flip flop circuit for diving a frequency of the referential rectangular wave by two and producing a non-inverted rectangular wave and an inverted rectangular wave, a first integrating circuit and a second integrating circuit for integrating levels of the inverted rectangular wave and the non-inverted rectangular wave produced in the flip flop circuit respectively and producing chopping waves respectively, and a first comparing circuit and a second comparing circuit for comparing levels of the chopping waves produced in the first integrating circuit and the second integrating circuit with a feed-back voltage sent from a feed-back circuit respectively and outputting control signals to a first switching circuit and a second switching circuit respectively.
Therefore, because a non-inverted chopping wave and an inverted chopping wave are produced in the first integrating circuit and the second integrating circuit after the non-inverted rectangular wave and the inverted rectangular wave are produced in the flip flop circuit, an electric-discharge lamp lighting apparatus operable at high speed can be obtained at low cost without using a circuit for inverting any chopping wave. Also, because a frequency of the referential rectangular wave is divided by two in the flip flop circuit, a duty ratio of the rectangular wave produced in the flip flop circuit is set to 50%. Therefore, no DC offset occurs in the produced chopping waves, and the control signals set with high accuracy can be output.
An electric-discharge lamp lighting apparatus according to the present invention written in claim 3 of xe2x80x9cWHAT IS CLAIMED ISxe2x80x9d includes a comparing power source for generating a comparing voltage, a third comparing circuit and a fourth comparing circuit for comparing the comparing voltage with a first chopping wave and a second chopping wave respectively, an RS flip flop circuit for receiving output signals of the third comparing circuit and the fourth comparing circuit and producing a non-inverted rectangular wave and an inverted rectangular wave, a first integrating circuit and a second integrating circuit for integrating levels of the inverted rectangular wave and the non-inverted rectangular wave produced in the RS flip flop circuit respectively to produce the first chopping wave and the second chopping wave and supplying the first chopping wave and the second chopping wave to the third comparing circuit and the fourth comparing circuit respectively, and a first comparing circuit and a second comparing circuit for comparing levels of the chopping waves produced in the first integrating circuit and the second integrating circuit respectively with a feed-back voltage sent from a feed-back circuit and outputting control signals to a first switching circuit and a second switching circuit respectively.
Therefore, because a non-inverted chopping wave and an inverted chopping wave are produced in the first integrating circuit and the second integrating circuit after the non-inverted rectangular wave and the inverted rectangular wave are produced in the RS flip flop circuit, an electric-discharge lamp lighting apparatus operable at high speed can be obtained at low cost without using a circuit for inverting any chopping wave. Also, a result of a comparison between the first produced chopping wave and the comparing voltage is obtained, a result of a comparison between the second produced chopping wave and the comparing voltage is obtained, and a self-oscillating type is adopted by feeding back the comparison results to the RS flip flop circuit. Therefore, a DC offset between the chopping waves does not occur due to each constituent element of the first and second integrating circuits not correctly set to a designed function. Accordingly, the chopping waves symmetric to each other with respect to the wave height value can be obtained, and the control signals set with high accuracy can be output.
In an electric-discharge lamp lighting apparatus according to the present invention written in claim 4 of xe2x80x9cWHAT IS CLAIMED ISxe2x80x9d, the first integrating circuit includes a first resisting element and a common condenser, the second integrating circuit includes a second resisting element and the common condenser, and the common condenser is connected with both an output terminal of the first resisting element and an output terminal of the second resisting element in parallel connection.
Therefore, because the condenser is used for the first integrating circuit and the second integrating circuit in common, as compared with a case where a condenser is arranged in each of the first integrating circuit and the second integrating circuit, the total configuration of the first integrating circuit and the second integrating circuit can be simplified, and the asymmetry between the chopping waves due to each condenser not correctly set to a designed function can be suppressed.
In an electric-discharge lamp lighting apparatus according to the present invention written in claim 5 of xe2x80x9cWHAT IS CLAIMED ISxe2x80x9d, the first integrating circuit includes a first condenser in which one end is connected with the output terminal of the first resisting element and the other end is grounded, and the second integrating circuit further comprises a second condenser in which one end is connected with the output terminal of the second resisting element and the other end is grounded.
Therefore, the condensers 34a and 35a are arranged in the integrating circuits 22 and 26 respectively to reduce the distortion of the chopping waves, and the distortion of the chopping waves occurring due to a phase difference between the non-inverted rectangular wave and the inverted rectangular wave produced in the RS flip flop circuit can be reduced by the function of the first and second condensers. Here, capacities of the first and second condensers can be set to xc2xd of a capacity of the common condenser, and adverse influence caused by the first and second condensers not accurately set to designed functions can be reduced.
An electric-discharge lamp lighting apparatus according to the present invention written in claim 6 of xe2x80x9cWHAT IS CLAIMED ISxe2x80x9d includes a switching circuit, connected with the third comparing circuit and the RS flip flop circuit, for performing an on-off control according to an output signal of the fourth comparing circuit.
Therefore, even though the output signals of the third and fourth comparing circuits are set to the L level together at an operation start time, the third switching circuit performs an off control to set one input signal of the RS flip flop circuit to the H level. Therefore, the normal operation of the RS flip flop circuit can be performed.
In an electric-discharge lamp lighting apparatus according to the present invention written in claim 7 of xe2x80x9cWHAT IS CLAIMED ISxe2x80x9d, the comparing power source is formed of a variable power source, and the comparing voltage generated in the variable power source is arbitrarily adjustable.
Therefore, the output signals of the third and fourth comparing circuits can be adjusted according to the adjustment of the comparing voltage, and the cycle of each chopping wave generated can be arbitrarily adjusted.
In an electric-discharge lamp lighting apparatus according to the present invention written in claim 8 of xe2x80x9cWHAT IS CLAIMED ISxe2x80x9d, the RS flip flop circuit is formed of a logic gate integrated circuit.
Therefore, the RS flip flop circuit can be easily formed of the logic gate integrated circuit.